Electrode assemblies

ABSTRACT

Provided herein is an electrode assembly of lithium-ion battery, comprising at least one anode, at least one cathode and at least one separator interposed between the at least one anode and at least one cathode, wherein the water content of the electrode assembly is less than 20 ppm by weight, based on the total weight of the electrode assembly.

FIELD OF THE INVENTION

The present invention relates to the field of batteries. In particular,this invention relates to methods for drying electrode assemblies oflithium-ion batteries and electrode assemblies made by the methodsdisclosed herein.

BACKGROUND OF THE INVENTION

Lithium-ion batteries (LIBs) have attracted extensive attention in thepast two decades for a wide range of applications in portable electronicdevices such as cellular phones and laptop computers. Due to rapidmarket development of electric vehicles (EV) and grid energy storage,high-performance, low-cost LIBs are currently offering one of the mostpromising options for large-scale energy storage devices.

Currently, electrodes are prepared by dispersing fine powders of anactive battery electrode material, a conductive agent, and a bindermaterial in an appropriate solvent. The dispersion can be coated onto acurrent collector such as a copper or aluminum metal foil, and thendried at an elevated temperature to remove the solvent. Sheets of thecathode and anode are subsequently stacked or rolled with the separatorseparating the cathode and anode to form a battery.

The lithium-ion battery manufacturing process is sensitive to moisture.A battery with high water content leads to serious attenuation ofelectrochemical performance and affects stability of battery. Therefore,environmental humidity must be controlled strictly for the productionprocess of LIBs. Most of the LIBs are produced in an environment withless than 1 percent humidity. However, significant cost is incurredbecause of the stringent moisture-free process. To address the moisturesensitive issue of electrode assembly, it is important to dry theelectrode assembly prior to electrolyte filing so as to reduce the watercontent in the battery.

Chinese Patent No. 104142045 B describes a method of drying an electrodeassembly of LIBs. The method comprises heating an electrode assemblyunder vacuum at a temperature of 30-100° C.; filling the oven with dryair or inert gas; repeating these two steps for 1-10 times. This methodprovides the electrode assembly with a water content between 430.5 ppmand 488.1 ppm.

Chinese Patent Application No. 105115250 A describes a method of dryingan electrode assembly of LIBs. The method comprises heating an electrodeassembly under vacuum at a temperature of 85±5° C.; filling the ovenwith hot, dry nitrogen gas; repeating these two steps for 10-20 times.This method provides the electrode assembly with a water content of lessthan 200 ppm.

Chinese Patent No. 102735023 B describes a method of drying an electrodeassembly of LIBs. The method comprises heating an electrode assemblyunder vacuum at a temperature of 20-70° C.; filling the oven with dryair or nitrogen gas; repeating these two steps for 5-50 times. Thismethod provides the electrode assembly with a water content between110.1 ppm and 137.2 ppm.

Chinese Patent No. 103344097 B describes a method of drying an electrodeassembly of LIBs. The method comprises heating an electrode assemblyunder vacuum at a temperature of 75-85° C.; filling the oven with anon-oxidizing gas; heating the electrode assembly to 75-85° C.; vacuumdrying the electrode assembly again. However, this method does notprovide the water content of the dried electrode assembly for evaluatingthe drying process.

The water contents of the electrode assemblies as dried by the existingmethods range from a hundred ppm to several hundreds ppm, which mayaffect the cycling stability and rate capability of LIBs. In view of theabove, there is always a need for electrode assemblies having a lowwater content.

SUMMARY OF THE INVENTION

The aforementioned needs are met by various aspects and embodimentsdisclosed herein.

In one aspect, provided herein is an electrode assembly for a nonaqueouselectrolyte secondary battery, comprising at least one anode, at leastone cathode and at least one separator interposed between the at leastone anode and at least one cathode, wherein the water content of theelectrode assembly is less than 20 ppm by weight, based on the totalweight of the electrode assembly.

In certain embodiments, the at least one cathode comprises a cathodecurrent collector and a cathode electrode layer comprising a cathodematerial, a binder material and a conductive agent, and the at least oneanode comprises an anode current collector and an anode electrode layercomprising an anode material, a binder material and a conductive agent,wherein each of the cathode and anode electrode layers independently hasa void volume of less than 40%, less than 35%, less than 33%, less than30%, less than 25%, less than 20%, less than 18%, less than 15%, lessthan 13%, less than 10%, or less than 8%, based on the total volume ofthe electrode layer.

In some embodiments, the density of each of the cathode and anodeelectrode layers is independently from about 1.0 g/cm³ to about 6.5g/cm³ or from about 1.0 g/cm³ to about 3.0 g/cm³.

In certain embodiments, the thickness of each of the cathode and anodeelectrode layers is independently from about 1.0 μm to about 40 μm orfrom about 1.0 μm to about 25 μm.

In some embodiments, the at least one separator is made of polymericfibers selected from the group consisting of polyolefin, polyethylene,high-density polyethylene, linear low-density polyethylene, low-densitypolyethylene, ultrahigh-molecular-weight polyethylene, polypropylene,polypropylene/polyethylene co-polymer, polybutylene, polypentene,polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone,polysulfones, polyphenylene oxide, polyphenylene sulfide,polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyvinylpyrrolidone, polyester, polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalene, polybutylene naphthalate, andcombinations thereof.

In certain embodiments, the thickness of the separator is from about 1.0μm to about 40 μm or from about 1.0 μm to about 25 μm.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from the groupconsisting of styrene-butadiene rubber, acrylated styrene-butadienerubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrilebutadiene rubber, acrylonitrile-styrene-butadiene copolymer, acrylrubber, butyl rubber, fluorine rubber, polytetrafluoroethylene,polyethylene, polypropylene, ethylene/propylene copolymers,polybutadiene, polyethylene oxide, chlorosulfonated polyethylene,polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinylacetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile,polystyrene, latex, acrylic resins, phenolic resins, epoxy resins,carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate,cellulose acetate butyrate, cellulose acetate propionate,cyanoethylcellulose, cyanoethylsucrose, polyester, polyamide, polyether,polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid,polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide,polyurethane, fluorinated polymer, chlorinated polymer, a salt ofalginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof.

In certain embodiments, each of the binder materials in the cathode andanode electrode layers is independently present in an amount from 2% to10% by weight, based on the total weight of the electrode layer.

In some embodiments, the cathode material is selected from the groupconsisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Co_(1−x−y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂,LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, and combinationsthereof, wherein each x is independently from 0.3 to 0.8; each y isindependently from 0.1 to 0.45; and each z is independently from 0 to0.2.

In certain embodiments, each of the conductive agents in the cathode andanode electrode layers is independently selected from the groupconsisting of carbon, carbon black, graphite, expanded graphite,graphene, graphene nanoplatelets, carbon fibres, carbon nano-fibers,graphitized carbon flake, carbon tubes, carbon nanotubes, activatedcarbon, mesoporous carbon, and combinations thereof.

In some embodiments, each of the conductive agents in the cathode andanode electrode layers is independently present in an amount from 2% to10% by weight, based on the total weight of the electrode layer.

In certain embodiments, the anode material is selected from the groupconsisting of natural graphite particulate, synthetic graphiteparticulate, Sn particulate, Li₄Ti₅O₁₂ particulate, Si particulate, Si—Ccomposite particulate, and combinations thereof.

In some embodiments, each of the current collectors of the at least onecathode and anode is independently stainless steel, titanium, nickel,aluminum, copper, or electrically-conductive resin.

In certain embodiments, the current collector of the at least onecathode is an aluminum thin film, and wherein the current collector ofthe at least one anode is a copper thin film.

In some embodiments, the at least one anode and at least one cathode inthe electrode assembly have a water content of less than 20 ppm byweight, based on the total weight of the at least one anode and at leastone cathode.

In certain embodiments, the at least one separator in the electrodeassembly has a water content of less than 20 ppm by weight, based on thetotal weight of the at least one separator.

In another aspect, provided herein is a lithium battery comprising theelectrode assembly prepared by the method disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 2.

FIG. 2 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 4.

FIG. 3 depicts cycling performance of an electrochemical cell containingan electrode assembly prepared by the method described in Example 6.

DETAILED DESCRIPTION OF THE INVENTION

Provided herein is an electrode assembly for a nonaqueous electrolytesecondary battery, comprising at least one anode, at least one cathodeand at least one separator interposed between the at least one anode andat least one cathode, wherein the water content of the electrodeassembly is less than 20 ppm by weight, based on the total weight of theelectrode assembly.

The term “electrode” refers to a “cathode” or an “anode.”

The term “positive electrode” is used interchangeably with cathode.Likewise, the term “negative electrode” is used interchangeably withanode.

The term “void volume” refers to the volume of the spaces between thesolid materials in the electrode layer. The greater the void volume, themore electrolyte is retained in the electrode layer.

The term “binder material” refers to a chemical or a substance that canbe used to hold the electrode material and conductive agent in place.

The term “water-based hinder material” refers to a water-soluble orwater-dispersible binder polymer. Some non-limiting examples of thewater-based binder material include styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, acrylonitrile-butadiene rubber, acryl rubber,butyl rubber, fluorine rubber, polytetrafluoroethylene, polyethylene,polypropylene, ethylene/propylene copolymers, polybutadiene,polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin,polyphosphazene, polyacrylonitrile, polystyrene,ethylene/propylene/diene copolymers, polyvinylpyridine, chlorosulfonatedpolyethylene, latex, polyester resins, acrylic resins, phenolic resins,epoxy resins, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylcellulose, and combinations thereof.

The term “organic-based binder material” refers to a binder dissolved ordispersed in an organic solvent, in particular, N-methyl pyrrolidone(NMP). Some non-limiting examples of the organic-based binder materialinclude polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA),polyvinylidene fluoride (PVDF), copolymer of tetrafluoroethylene (TFE)and hexafluoropropylene (HFP), fluorinated ethylene-propylene (FEP)copolymer, and terpolymer of tetrafluoroethylene, hexafluoropropyleneand vinylidene fluoride, and combinations thereof.

The term “current collector” refers to a support for coating theelectrode material and a chemically inactive high electron conductor forkeeping an electric current flowing to electrodes during discharging orcharging a secondary battery.

The term “conductive agent” refers to a material which is chemicallyinactive and has good electrical conductivity. Therefore, the conductiveagent is often mixed with an electrode active material at the time offorming an electrode to improve electrical conductivity of theelectrode. In some embodiments, the conductive agent is a carbonaceousmaterial.

The term “electrode assembly” refers to a structure comprising at leastone positive electrode, at least one negative electrode, and at leastone separator interposed between the positive electrode and the negativeelectrode.

The term “room temperature” refers to indoor temperatures from about 18°C. to about 30° C., e.g., 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,29, or 30° C. In some embodiments, room temperature refers to atemperature of about 20° C.+/−1° C. or +/−2° C. or +/−3° C. In otherembodiments, room temperature refers to a temperature of about 22° C. orabout 25° C.

The term “C rate” refers to the charging or discharging rate of a cellor battery, expressed in terms of its total storage capacity in Ah ormAh. For example; a rate of 1 C means utilization of all of the storedenergy in one hour; a 0.1 C means utilization of 10% of the energy inone hour or full energy in 10 hours; and a 5 C means utilization of fullenergy in 12 minutes.

The term “ampere-hour (Ah)” refers to a unit used in specifying thestorage capacity of a battery. For example, a battery with 1 Ah capacitycan supply a current of one ampere for one hour or 0.5 A for two hours,etc. Therefore, 1 Ampere-hour (Ah) is the equivalent of 3600 coulombs ofelectrical charge. Similarly, the term “miniampere-hour (mAh)” alsorefers to a unit of the storage capacity of a battery and is 1/1,000 ofan ampere-hour.

The term “battery cycle life” refers to the number of completecharge/discharge cycles a battery can perform before its nominalcapacity falls below 80% of its initial rated capacity.

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or “approximate”is used in connection therewith. They may vary by 1 percent, 2 percent,5 percent, or, sometimes, 10 to 20 percent. Whenever a numerical rangewith a lower limit, R^(L), and an upper limit, R^(U), is disclosed, anynumber falling within the range is specifically disclosed. Inparticular, the following numbers within the range are specificallydisclosed: R=R^(L)+k*(R^(U)−R^(L)), wherein k is a variable ranging from1 percent to 100 percent with a 1 percent increment, i.e., k is 1percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent,51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98percent, 99 percent, or 100 percent. Moreover, any numerical rangedefined by two R numbers as defined in the above is also specificallydisclosed.

Generally, lithium-ion battery manufacturing processes are carried outin dry rooms where the environment must be carefully controlled topreserve optimum production conditions. The dew point of the air is anindicator of the quality of the dry room. Typical dew point values forbattery production range from −40° C. to −65° C. Efficiency and servicelife of a battery are determined in the cell production stage.Nevertheless, no prior art document describes a method for achieving anelectrode assembly having a particularly low water content (e.g. lessthan 20 ppm).

An electrode assembly can be constructed by sequentially stacking atleast one negative electrode, at least one separator, and at least onepositive electrode. The number and arrangement of the at least onepositive electrode, the at least one negative electrode, and the atleast one separator, for configuring the electrode assembly are notparticularly limited. In some embodiments, the electrode assembly has astacked structure in which two outermost electrodes comprise an opposingpolarities (i.e., a positive electrode and a negative electrode), suchas a positive electrode/separator/negative electrode structure or apositive electrode/separator/negative electrode/separator/positiveelectrode/separator/negative electrode structure.

In certain embodiments, the electrode assembly has a stacked structurein which two outermost electrodes comprise the same polarity (i.e.,positive electrodes or negative electrodes), such as a positiveelectrode/separator/negative electrode/separator/positive electrodestructure or a negative electrode/separator/positiveelectrode/separator/negative electrode structure.

In some embodiments, the electrode assembly has a structure in which aseparator is disposed on one of the outermost sides, such as aseparator/positive electrode/separator/negative electrode structure or apositive electrode/separator/negative electrode/separator structure. Inother embodiments, the electrode assembly has a structure in whichseparators are disposed on both the outermost sides, such as aseparator/positive electrode/separator/negative electrode/separatorstructure.

In certain embodiments, the electrode assembly is assembled under stricthumidity control in which the air has a dew point of −65° C. In someembodiments, the electrode assembly is assembled under dry conditions inwhich the air has a dew point of −50° C., −40° C., −30° C., −20° C.,−10° C., 0° C., 5° C., or 10° C. In certain embodiments, the electrodeassembly is assembled in the open air with no control of humidity.

The separator disposed between the opposing active anode and cathodesurfaces can prevent contact between the anode and cathode and a shortcircuit of the lithium-ion battery. In some embodiments, the separatormay comprise woven or nonwoven polymeric fibers, natural fibers, carbonfibers, glass fibers or ceramic fibers. In certain embodiments, theseparator comprises woven or nonwoven polymeric fibers.

In some embodiments, the fibers of the nonwoven or woven are made oforganic polymers, such as polyolefin, polyethylene, high-densitypolyethylene, linear low-density polyethylene, low-density polyethylene,ultrahigh-molecular-weight polyethylene, polypropylene,polypropylene/polyethylene co-polymer, polybutylene, polypentene,polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone,polysulfones, polyphenylene oxide, polyphenylene sulfide,polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyvinylpyrrolidone, polyester, polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalene, polybutylene naphthalate,derivatives thereof, or a combination thereof. In certain embodiments,the separator is made of polyolefinic fibers selected from the groupconsisting of polyethylene, high-density polyethylene, linearlow-density polyethylene, low-density polyethylene,ultrahigh-molecular-weight polyethylene, polypropylene,polypropylene/polyethylene co-polymer, and combinations thereof. In someembodiments, the separator is made of polymeric fibers selected from thegroup consisting of polyester, polyacetal, polyamide, polycarbonate,polyimide, polyetherether ketone, polyether sulfone, polyphenyleneoxide, polyphenylene sulfide, polyethylene naphthalene, and combinationsthereof. In other embodiments, the polymeric fiber is not polyethylene,high-density polyethylene, linear low-density polyethylene, low-densitypolyethylene, ultrahigh-molecular-weight polyethylene, polypropylene, orpolypropylene/polyethylene co-polymer. In further embodiments, thepolymeric fiber is not polyacetal, polyether sulfone, polyphenyleneoxide, polyphenylene sulfide, or polycarbonate. In still furtherembodiments, polymeric fiber is not polyamide, polyimide, orpolyetherether ketone. But all other known polymeric fibers and manynatural fibers can be used as well.

In certain embodiments, the separator disclosed herein has a meltingpoint of 100° C. or higher, 120° C. or higher, 140° C. or higher, 160°C. or higher, 180° C. or higher, 200° C. or higher, or 250° C. orhigher. In some embodiments, the separator disclosed herein has amelting point of 140° C. or higher, 160° C. or higher, 180° C. orhigher, 200° C. or higher, or 250° C. or higher. The separator havinghigh melting point shows high thermal stability and therefore can bedried at high temperature without thermally shrinking. This also allowsthe drying to be more efficiently performed. Therefore, the electrodeassembly can be dried in a relatively short time, resulting in a shortproduction time.

The separator can be in a coated or uncoated form. In some embodiments,the separator has a thickness from about 10 μm to about 200 μm, fromabout 30 μm to about 100 μm, from about 10 μm to about 75 μm, from about10 μm to about 50 μm, from about 10 μm to about 20 μm, from about 15 μmto about 40 μm, from about 15 μm to about 35 μm, from about 20 μm toabout 40 μm, from about 20 μm to about 35 μm, from about 20 μm to about30 μm, from about 30 μm to about 60 μm, from about 30 μm to about 50 μm,or from about 30 μm to about 40 μm.

In certain embodiments, the separator has a thickness of about 15 μm,about 20 μm, or about 25 μm. In some embodiments, the separator of thepresent invention has a thickness of less than 40 μm, less than 35 μm,less than 30 μm, less than 25 μm, or less than 20 μm. If the separatoris sufficiently thin, the moisture may be evaporated at high dryingrates.

In some embodiments, the electrode assembly is loosely stacked. In theloosely stacked electrode assembly, there is a void space between theelectrode layer and separator layer, allowing moisture to escape.Therefore, the loosely stacked electrode assembly can be effectivelydried in a short period of time. On the other hand, when the electrodeassembly is pressed under pressure before drying, the tightly packedelectrode assembly has little or no void space between the electrodelayer and separator layer, thus reducing airflow and drying efficiency.

In certain embodiments, the positive electrode, separator and negativeelectrode are stacked and spirally wound into a jelly-roll configurationbefore drying. Since a roll electrode assembly is tightly packed, thereis also little or no void space between the electrode layer andseparator layer, thus reducing airflow and drying efficiency.

A positive electrode includes a cathode electrode layer supported on acathode current collector. The cathode electrode layer comprises atleast a cathode material and a binder material. The cathode electrodelayer may further comprise a conductive agent for enhancing electronconductivity of the cathode electrode layer. A negative electrodeincludes an anode electrode layer supported on an anode currentcollector. The anode electrode layer comprises at least an anodematerial and a binder material. The anode electrode layer may furthercomprise a conductive agent for enhancing electron conductivity of theanode electrode layer.

In some embodiments, the at least one cathode comprises a cathodecurrent collector and a cathode electrode layer comprising a cathodematerial, a binder material and a conductive agent, and the at least oneanode comprises an anode current collector and an anode electrode layercomprising an anode material, a binder material and a conductive agent,wherein each of the cathode and anode electrode layers independently hasa void volume of less than 40%, less than 37%, less than 35%, less than33%, less than 30%, less than 25%, less than 20%, less than 18%, lessthan 15%, less than 13%, less than 10%, or less than 8%, based on thetotal volume of the cathode or anode electrode layer. In certainembodiments, the void volume of the electrode layer is between 8% and40%, between 8% and 35%, between 8% and 30%, between 10% and 30%,between 13% and 30%, between 13% and 33%, between 15% and 30%, between18% and 30%, between 20% and 30%, or between 25% and 30%, based on thetotal volume of the cathode or anode electrode layer.

If the void volume of the electrode layer is 35% or more, both theenergy density and power output of the battery are low. When the voidvolume of the electrode layer is between 10% and 35%, the batteryexhibits good diffusibility of lithium ions and high-output performance.

The current collector acts to collect electrons generated byelectrochemical reactions of the active battery electrode material or tosupply electrons required for the electrochemical reactions. In someembodiments, each of the cathode and anode current collectors, which canbe in the form of a foil, sheet or film, is independently stainlesssteel, titanium, nickel, aluminum, copper or electrically-conductiveresin. In certain embodiments, the cathode current collector is analuminum thin film. In some embodiments, the anode current collector isa copper thin film.

In some embodiments, the current collector has a thickness from about 6μm to about 100 μm. Thickness of the current collector will affect thevolume occupied by the current collector within a battery and the amountof the electrode material and hence the capacity in the battery.

In certain embodiments, the thickness of each of the cathode and anodeelectrode layers on the current collector is independently from about 1μm to about 300 μm, from about 10 μm to about 300 μm, from about 20 μmto about 100 μm, from about 1 μm to about 100 μm, from about 1 μm toabout 50 μm, from about 1 μm to about 40 μm, from about 10 μm to about40 μm, from about 10 μm to about 30 μm, or from about 10 μm to about 25μm. In some embodiments, the thickness of the electrode layer on thecurrent collector is about 10 μm, about 15 μm, about 20 μm, about 25 μm,about 30 μm, about 35 μm, or about 40 μm.

In some embodiments, the density of each of the cathode and anodeelectrode layers on the current collector is independently from about1.0 g/cm³ to about 6.5 g/cm³, from about 1.0 g/cm³ to about 5.0 g/cm³,from about 1.0 g/cm³ to about 4.0 g/cm³, from about 1.0 g/cm³ to about3.5 g/cm³, from about 1.0 g/cm³ to about 3.0 g/cm³, from about 1.0 g/cm³to about 2.0 g/cm³, from about 2.0 g/cm³ to about 5.0 g/cm³, from about2.0 g/cm³ to about 4.0 g/cm³, from about 3.0 g/cm³ to about 5.0 g/cm³ orfrom about 3.0 g/cm³ to about 6.0 g/cm³. Similarly, an increase in thedensity of the electrode layer will result in a reduction of void volumein the final electrode coating and a denser electrode, thereby achievingdesired battery capacity.

In certain embodiments, the cathode material is selected from the groupconsisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Co_(1−x−y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂,LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, and combinationsthereof, wherein each x is independently from 0.3 to 0.8; each y isindependently from 0.1 to 0.45; and each z is independently from 0 to0.2. In certain embodiments, the cathode material is selected from thegroup consisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Co_(1−x−y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂,LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, and combinationsthereof, wherein each x is independently from 0.4 to 0.6; each y isindependently from 0.2 to 0.4; and each z is independently from 0 to0.1. In other embodiments, the cathode material is not LiCoO₂, LiNiO₂,LiV₂O₅, LiTiS₂, LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, or LiFePO₄. Infurther embodiments, the cathode material is not LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Mn_(y)Co_(1−x−y)O₂, or LiNi_(x)Co_(v)Al_(z)O₂, whereineach x is independently from 0.3 to 0.8; each y is independently from0.1 to 0.45; and each z is independently from 0 to 0.2.

In some embodiments, the anode material is selected from the groupconsisting of natural graphite particulate, synthetic graphiteparticulate, Sn (tin) particulate, Li₄Ti₅O₁₂ particulate, Si (silicon)particulate, Si—C composite particulate, and combinations thereof. Inother embodiments, the anode material is not natural graphiteparticulate, synthetic graphite particulate, Sn (tin) particulate,Li₄Ti₅O₁₂ particulate, Si (silicon) particulate, or Si—C compositeparticulate.

In certain embodiments, the amount of each of the cathode and anodematerials is independently at least 50%, at least 55%, at least 60%, atleast 65%, at least 70%, at least 75%, at least 80%, at least 85%, atleast 90%, or at least 95% by weight, based on the total weight of thecathode or anode electrode layer. In some embodiments, the amount ofeach of the cathode and anode materials is independently at most 50%, atmost 55%, at most 60%, at most 65%, at most 70%, at most 75%, at most80%, at most 85%, at most 90%, or at most 95% by weight, based on thetotal weight of the cathode or anode electrode layer.

In some embodiments, the conductive agent is selected from the groupconsisting of carbon, carbon black, graphite, expanded graphite,graphene, graphene nanoplatelets, carbon fibres, carbon nano-fibers,graphitized carbon flake, carbon tubes, carbon nanotubes, activatedcarbon, mesoporous carbon, and combinations thereof. In certainembodiments, the conductive agent is not carbon, carbon black, graphite,expanded graphite, graphene, graphene nanoplatelets, carbon fibres,carbon nano-fibers, graphitized carbon flake, carbon tubes, carbonnanotubes, activated carbon, or mesoporous carbon.

In certain embodiments, the amount of the conductive agent in each ofthe cathode and anode electrode layers is independently at least 1%, atleast 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least15%, at least 20%, at least 25%, at least 30%, at least 35%, at least40%, at least 45%, or at least 50% by weight, based on the total weightof the cathode or anode electrode layer. In some embodiments, the amountof the conductive agent in each of the cathode and anode electrodelayers is independently at most 1%, at most 2%, at most 3%, at most 4%,at most 5%, at most 10%, at most 15%, at most 20%, at most 25%, at most30%, at most 35%, at most 40%, at most 45%, or at most 50% by weight,based on the total weight of the cathode or anode electrode layer.

In some embodiments, the amount of the conductive agent in each of thecathode and anode electrode layers is independently from about 0.05 wt.% to about 0.5 wt. %, from about 0.1 wt. % to about 1 wt. %, from about0.25 wt. % to about 2.5 wt. %, from about 0.5 wt. % to about 5 wt. %,from about 2 wt. % to about 5 wt. %, from about 3 wt. % to about 7 wt.%, or from about 5 wt. % to about 10 wt. %, based on the total weight ofthe cathode or anode electrode layer.

After assembling the electrode assembly, the electrode assembly isplaced into a drying chamber. In some embodiments, the drying chamber isconnected to a vacuum pump, so that the pressure in the chamber can bereduced. The pressure is reduced sufficiently so as to lower the boilingpoint of water. The drying time can therefore be considerably reduced.In certain embodiments, the drying chamber is connected to a centralvacuum supply, thereby allowing several vacuum drying ovens to beoperated simultaneously. In some embodiments, the number of vacuumdrying ovens connected to a central vacuum supply ranges from 1 to 20depending on the number of pumps operated. In certain embodiments, avacuum pump or central vacuum supply is connected to the drying chamberby a suction line equipped with a gas outlet valve. In some embodiments,the drying chamber is also connected to a gas reservoir containing dryair or inert gas by a duct equipped with a gas inlet valve. When the gasoutlet valve is closed and the gas inlet valve is opened, vacuum is lostin the drying chamber. The valve might be of a solenoid or needle typeor a mass flow controller. Any devices allowing an appropriate flowadjustment might be used.

To reduce the power required for the pumps, a condenser can be providedbetween the drying chamber and the pump. The condenser condenses outwater vapor, which is then separated.

In certain embodiments, the electrode assembly can be dried under vacuumat a temperature from about 70° C. to about 155° C., from about 80° C.to about 155° C., from about 90° C. to about 155° C., from about 100° C.to about 155° C., from about 100° C. to about 140° C., from about 100°C. to about 130° C., from about 100° C. to about 120° C., from about100° C. to about 110° C., or from about 110° C. to about 130° C. Incertain embodiments, the electrode assembly can be dried under vacuum ata temperature from about 80° C. to about 155° C. In some embodiments,the electrode assembly can be dried under vacuum at a temperature ofabout 80° C. or higher, 90° C. or higher, 100° C. or higher, 110° C. orhigher, 120° C. or higher, 130° C. or higher, 140° C. or higher, or 150°C. or higher. In certain embodiments, the electrode assembly can bedried under vacuum at a temperature of less than 155° C., less than 150°C., less than 145° C., less than 140° C., less than 135° C., less than130° C., less than 125° C., less than 120° C., less than 115° C., lessthan 110° C., less than 105° C., less than 100° C., or less than 90° C.

In some embodiments, the time period for drying the electrode assemblyunder vacuum is from about 5 minutes to about 12 hours, from about 5minutes to about 4 hours, from about 5 minutes to about 2 hours, fromabout 5 minutes to about 1 hour, from about 5 minutes to about 30minutes, from about 5 minutes to about 15 minutes, from about 15 minutesto about 1 hour, from about 15 minutes to about 3 hours, from about 1hour to about 10 hours, from about 1 hour to about 8 hours, from about 1hour to about 6 hours, from about 1 hour to about 4 hours, from about 1hour to about 2 hours, from about 2 hours to about 12 hours, from about2 hours to about 8 hours, from about 2 hours to about 5 hours, fromabout 2 hours to about 3 hours, or from about 4 hours to about 12 hours.In some embodiments, the time period for drying the electrode assemblyunder vacuum is from about 5 minutes to about 2 hours, or from about 15minutes to about 30 minutes.

Any vacuum pumps that can reduce the pressure of the drying chamber canbe used herein. Some non-limiting examples of the vacuum pumps includedry vacuum pumps, turbo pumps, rotary vane vacuum pumps, cryogenicpumps, and sorption pumps.

In some embodiments, the vacuum pump is an oil free pump. The oil freepump operates without the need for oil in the pump parts which areexposed to gases being pumped, or partial vacuum. Thus, any gasesbackstreaming through the pump are free from oil vapour. Progressive oilvapour deposited on surfaces of the electrode assembly may reduce theelectrochemical performance of a battery. An example of such pump is adiaphragm vacuum pump.

In certain embodiments, high vacuum can be achieved by using a two-stagepumping system to evacuate the drying chamber. The pumping systemcomprises a primary vacuum pump such as a rotary pump or diaphragm pumparranged in series with a high vacuum pump such as a turbo-molecularpump.

In some embodiments, the electrode assembly is dried under atmosphericpressure. In certain embodiments, the drying is performed in a vacuumstate. In further embodiments, the vacuum state is maintained at apressure within the range from about 1×10⁻¹ Pa to about 1×10⁻⁴ Pa, fromabout 10 Pa to about 1×10⁻¹ Pa, from about 1×10³ Pa to about 10 Pa, orfrom about 2.5×10⁴ Pa to about 1×10³ Pa. In still further embodiments,the vacuum state is at a pressure of about 1×10³ Pa, about 2×10³ Pa,about 5×10³ Pa, about 1×10⁴ Pa, or about 2×10⁴ Pa.

After a predetermined drying time period, the drying chamber ventsdirectly to a gas reservoir containing dry air or inert gas via a gasinlet valve. In some embodiments, the gas reservoir is a nitrogen gascylinder. In certain embodiments, the inert gas is selected from thegroup consisting of helium, argon, neon, krypton, xenon, nitrogen,carbon dioxide, and combinations thereof. In some embodiments, the watercontent of the dry air or inert gas is maintained less than or equal to10 ppm, less than or equal to 8 ppm, less than or equal to 5 ppm, lessthan or equal to 4 ppm, less than or equal to 3 ppm, less than or equalto 2 ppm, or less than or equal to 1 ppm.

In some embodiments, the dry air or inert gas is preheated beforeentering the drying chamber. In certain embodiments, the temperature ofthe dry air or inert gas is from about 70° C. to about 130° C., fromabout 70° C. to about 110° C., from about 70° C. to about 100° C., fromabout 70° C. to about 90° C., from about 70° C. to about 80° C., fromabout 80° C. to about 155° C., from about 80° C. to about 120° C., fromabout 80° C. to about 100° C., from about 90° C. to about 155° C., fromabout 90° C. to about 130° C., from about 90° C. to about 100° C., fromabout 70° C. to about 155° C., from about 100° C. to about 130° C., orfrom about 100° C. to about 120° C. In some embodiments, the dry air orinert gas is preheated to a temperature from about 70° C. to about 155°C. before entering the drying chamber.

In certain embodiments, the dry air or inert gas stays in the dryingchamber for a time period from about 30 seconds to about 2 hours, fromabout 1 minute to about 1 hour, from about 5 minutes to about 30minutes, from about 5 minutes to about 15 minutes, from about 5 minutesto about 10 minutes, from about 10 minutes to about 30 minutes, fromabout 10 minutes to about 20 minutes, from about 10 minutes to about 15minutes, from about 15 minutes to about 1 hour, from about 15 minutes toabout 30 minutes, from about 15 minutes to about 20 minutes, or fromabout 30 minutes to about 1 hour. In some embodiments, the dry air orinert gas stays in the drying chamber for a time period from about 30seconds to about 2 hours, from about 5 minutes to about 2 hours, or fromabout 15 minutes to about 30 minutes.

In some embodiments, the electrode assembly can be further dried undervacuum after incubating the electrode assembly with the dry gas for apredetermined time. This procedure can be repeated as many times asrequired to reduce the moisture content of the electrode assembly to anappropriate level. In certain embodiments, this procedure can berepeated around 2 to 50 times until the moisture content in theelectrode assembly is less than 40 ppm, less than 30 ppm, less than 20ppm, less than 15 ppm, less than 10 ppm, or less than 5 ppm, based onthe total weight of the dried electrode assembly.

In certain embodiments, the steps of vacuum drying and gas filling canbe repeated at least 2 times, at least 3 times, at least 4 times, atleast 5 times, at least 6 times, at least 7 times, at least 8 times, atleast 9 times, at least 10 times, at least 12 times, at least 14 times,at least 16 times, at least 18 times, at least 20 times, at least 22times, at least 24 times, at least 26 times, at least 28 times, or atleast 30 times. In some embodiments, the steps of vacuum drying and gasfilling can be repeated between 2 and 50 times, between 2 and 30 times,between 2 and 20 times, between 2 and 10 times, between 5 and 30 times,between 5 and 20 times, or between 2 and 10 times. In certainembodiments, the steps of vacuum drying and gas filling can be repeatedbetween 2 or more times.

In some embodiments, the process for drying the electrode assemblycomprises vacuum drying, followed by hot air drying. In someembodiments, the drying chamber blows hot air toward the electrodeassembly from above and/or underneath. In certain embodiments, the hotair drying is performed at an air velocity from about 1 meter/second toabout 50 meter/second, from about 1 meter/second to about 40meter/second, from about 1 meter/second to about 30 meter/second, fromabout 1 meter/second to about 20 meter/second, from about 1 meter/secondto about 10 meter/second, from about 10 meter/second to about 50meter/second, from about 10 meter/second to about 40 meter/second, fromabout 10 meter/second to about 30 meter/second, from about 10meter/second to about 20 meter/second, from about 20 meter/second toabout 30 meter/second, from about 30 meter/second to about 40meter/second, or from 40 meter/second to about 50 meter/second. In otherembodiments, a heated inert gas (i.e., helium, argon) is used instead ofheated air.

The drying gas might be preheated through heat exchange surfaces. Insome embodiments, the temperature of the hot air ranges from about 50°C. to about 155° C., from about 60° C. to about 150° C., from about 80°C. to about 150° C., from about 100° C. to about 150° C., from about 70°C. to about 150° C., from about 70° C. to about 130° C., from about 70°C. to about 100° C., from about 80° C. to about 150° C., from about 80°C. to about 130° C., from about 80° C. to about 110° C., from about 100°C. to about 140° C., or from about 100° C. to about 120° C.

In certain embodiments, the time period for hot air drying is from about1 minute to about 2 hours, from about 1 minute to about 1 hour, fromabout 1 minute to about 30 minutes, from about 1 minute to about 15minutes, from about 5 minutes to about 30 minutes, from about 5 minutesto about 20 minutes, from about 1 minute to about 15 minutes, from about5 minutes to about 10 minutes, from about 10 minutes to about 1 hour,from about 10 minutes to about 30 minutes, from about 10 minutes toabout 20 minutes, from about 15 minutes to about 1 hour, or from about15 minutes to about 30 minutes.

In some embodiments, the electrode assembly can be further dried undervacuum after blowing hot air for a predetermined time. This procedurecan be repeated as many times as required to reduce the moisture contentof the electrode assembly to an appropriate level, such as 40 ppm, 30ppm, 20 ppm, 15 ppm, 10 ppm, or 5 ppm.

Currently, water is the key factor needed to be strictly controlled inthe organic-based production process of lithium-ion batteries. A batterywith high water content may lead to serious attenuation ofelectrochemical performance and affect stability of battery.

The advantages of the present invention is that most of the fabricationcan take place outside a dry room. In some embodiments, the assemblingprocess can take place outside a dry room or a glove box. In certainembodiments, only the step for filling electrolyte or both the steps fordrying the electrode assembly and filing electrolyte are carried out ina dry room or a glove box. Thus, humidity control in the factory can beavoided, significantly lowering the investment cost.

The presence of moisture is detrimental to the operation of a battery.Generally, water content in the electrode assembly prepared byconventional methods contains an amount of water greater than 100 ppm byweight, based on the total weight of the electrode assembly. Even if theinitial battery performance is acceptable, the rate of deterioration ofthe battery performance may be unacceptable. To be able to achievesufficiently high battery performance, it would therefore beadvantageous to have a low water content in the battery.

The electrode assembly prepared by the method disclosed herein has aparticularly low water content, contributing to reliable performance ofthe lithium-ion batteries. In some embodiments, the water content in thedried electrode assembly is from about 5 ppm to about 50 ppm, from about5 ppm to about 40 ppm, from about 5 ppm to about 30 ppm, from about 5ppm to about 20 ppm, from about 5 ppm to about 10 ppm, from about 3 ppmto about 30 ppm, from about 3 ppm to about 20 ppm, or from about 3 ppmto about 10 ppm by weight, based on the total weight of the driedelectrode assembly.

In certain embodiments, the water content in the dried electrodeassembly is less than 50 ppm, less than 40 ppm, less than 30 ppm, lessthan 20 ppm, less than 10 ppm, less than 5 ppm, less than 4 ppm, lessthan 3 ppm, less than 2 ppm, or less than 1 ppm by weight, based on thetotal weight of the dried electrode assembly. In some embodiments, thedried electrode assembly disclosed herein has a water concentrationtherein no greater than about 5 ppm by weight, based on the total weightof the dried electrode assembly.

In some embodiments, the dried electrode assembly comprises at least onedried anode and at least one dried cathode, wherein the at least onedried anode and at least one dried cathode have a water content of lessthan 50 ppm, less than 40 ppm, less than 30 ppm, less than 20 ppm, lessthan 10 ppm, or less than 5 ppm by weight, based on the total weight ofthe at least one dried anode and at least one dried cathode.

In certain embodiments, the dried electrode assembly comprises at leastone dried separator, wherein the at least one dried separator has awater content of less than 50 ppm, less than 40 ppm, less than 30 ppm,less than 20 ppm, less than 10 ppm, or less than 5 ppm by weight, basedon the total weight of the at least one dried separator.

After the drying step, the electrode assembly can then be naturallycooled to 50° C. or less before being removed from the drying chamber.In some embodiments, the electrode assembly is cooled to 45° C. or less,40° C. or less, 35° C. or less, 30° C. or less, or 25° C. or less beforebeing removed from the drying chamber. In certain embodiments, theelectrode assembly is cooled to room temperature. In certainembodiments, the electrode assembly is cooled down by blowing a dry gasor inert gas in order to reach the target temperature more quickly.

The binder material in the electrode layer performs a role of bindingthe electrode material and conductive agent together on the currentcollector. In certain embodiments, each of the at least one anode and atleast one cathode independently comprises a binder material selectedfrom the group consisting of an organic-based binder material, awater-based binder material and a mixture of water-based andorganic-based binder materials.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from the groupconsisting of styrene-butadiene rubber, acrylated styrene-butadienerubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrilebutadiene rubber, acrylonitrile-styrene-butadiene copolymer, acrylrubber, butyl rubber, fluorine rubber, polytetrafluoroethylene,polyethylene, polypropylene, ethylene/propylene copolymers,polybutadiene, polyethylene oxide, chlorosulfonated polyethylene,polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinylacetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile,polystyrene, latex, acrylic resins, phenolic resins, epoxy resins,carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate,cellulose acetate butyrate, cellulose acetate propionate,cyanoethylcellulose, cyanoethylsucrose, polyester, polyamide, polyether,polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid,polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide,polyurethane, fluorinated polymer, chlorinated polymer, a salt ofalginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof. In furtherembodiments, the salt of alginic acid comprises a cation selected fromNa, Li, K, Ca, NH₄, Mg, Al, or a combination thereof.

In certain embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from the groupconsisting of styrene-butadiene rubber, carboxymethyl cellulose,polyvinylidene fluoride, acrylonitrile copolymer, polyacrylic acid,polyacrylonitrile, poly(vinylidene fluoride)-hexafluoropropene, latex, asalt of alginic acid, and combinations thereof.

In some embodiments, each of the binder materials in the cathode andanode electrode layers is independently selected from SBR, CMC, PAA, asalt of alginic acid, or a combination thereof. In certain embodiments,each of the binder materials in the cathode and anode electrode layersis independently acrylonitrile copolymer. In some embodiments, each ofthe binder materials in the cathode and anode electrode layers isindependently polyacrylonitrile. In certain embodiments, each of thebinder materials in the cathode and anode electrode layers independentlyis free of styrene-butadiene rubber, carboxymethyl cellulose,polyvinylidene fluoride, acrylonitrile copolymer, polyacrylic acid,polyacrylonitrile, poly(vinylidene fluoride)-hexafluoropropene, latex,or a salt of alginic acid.

In certain embodiments, the amount of the binder material in each of thecathode and anode electrode layers is independently at least 1%, atleast 2%, at least 3%, at least 4%, at least 5%, at least 10%, at least15%, at least 20%, at least 25%, at least 30%, at least 35%, at least40%, at least 45%, or at least 50% by weight, based on the total weightof the cathode or anode electrode layer. In some embodiments, the amountof the binder material in each of the cathode and anode electrode layersis independently at most 1%, at most 2%, at most 3%, at most 4%, at most5%, at most 10%, at most 15%, at most 20%, at most 25%, at most 30%, atmost 35%, at most 40%, at most 45%, or at most 50% by weight, based onthe total weight of the cathode or anode electrode layer.

In some embodiments, the amount of the binder material in each of thecathode and anode electrode layers is independently is from about 2 wt.% to about 10 wt. %, from about 3 wt. % to about 6 wt. %, from about 5wt. % to about 10 wt. %, from about 7.5 wt. % to about 15 wt. %, fromabout 10 wt. % to about 20 wt. %, from about 15 wt. % to about 25 wt. %,from about 20 wt. % to about 40 wt. %, or from about 35 wt. % to about50 wt. %, based on the total weight of the cathode or anode electrodelayer.

In order to prevent moisture from being present within the sealedcontainer, the step of filling electrolyte is carried out in a dry room.After drying, the electrode assembly is placed inside a container andthen an electrolyte is added to fill the pores of all of the layers ofseparator and electrodes, and each of the gaps between the positive andnegative electrodes and the separator in the electrode assembly under aninert atmosphere before sealing.

The method disclosed herein reduces the production costs of lithium-ionbatteries by consuming less energy and shortens manufacturing timesneeded for drying. Therefore, this method is especially suited forindustrial processes because of its low cost and ease of handling.

Also provided herein is a lithium battery comprising the electrodeassembly prepared by the method disclosed herein.

The following examples are presented to exemplify embodiments of theinvention. All numerical values are approximate. When numerical rangesare given, it should be understood that embodiments outside the statedranges may still fall within the scope of the invention. Specificdetails described in each example should not be construed as necessaryfeatures of the invention.

EXAMPLES

The water content in the electrode assembly was measured by Karl-fishertitration. The electrode assembly was cut into small pieces of 1 cm×1 cmin a glove box filled with argon gas. The cut electrode assembly havinga size of 1 cm×1 cm was weighed in a sample vial. The weighed electrodeassembly was then added into a titration vessel for Karl Fischertitration using Karl Fischer coulometry moisture analyzer (831 KFCoulometer, Metrohm, Switzerland). Measurement was repeated three timesto find the average value.

The water content in the electrodes or separator was measured byKarl-fisher titration. The electrode assembly was cut into small piecesof 1 cm×1 cm in a glove box filled with argon gas. The electrodeassembly was separated into the anode, cathode and separator layers. Thewater contents of the separated electrode layers and separator layerswere analysed separately by Karl Fischer titration. Measurement wasrepeated three times to find the average value.

Example 1

A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 94 wt. % cathodematerial (LNMC TLM 310, obtained from Xinxiang Tianli Energy Co. Ltd.,China), 3 wt. % carbon black (SuperP; obtained from Timcal Ltd, Bodio,Switzerland) as a conductive agent, and 0.8 wt. % polyacrylic acid (PAA,#181285, obtained from Sigma-Aldrich, US), 1.5 wt. % styrene butadienerubber (SBR, AL-2001, obtained from NIPPON A&L INC., Japan) and 0.7 wt.% polyvinylidene fluoride (PVDF; Solef® 5130, obtained from Solvay S.A.,Belgium) as a binder, which were dispersed in deionized water to form aslurry with a solid content of 50 wt. %. The slurry was homogenized by aplanetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm using a transfer coater (ZY-TSF6-6518,obtained from Jin Fan Zhanyu New Energy Technology Co. Ltd., China) withan area density of about 26 mg/cm². The coated films on the aluminumfoil were dried for 3 minutes by a 24-meter-long conveyor hot air dryingoven as a sub-module of the transfer coater operated at a conveyor speedof about 8 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of60° C. to the outlet temperature of 75° C. The electrode was thenpressed to increase the density of the coating and the density was 3.36g/cm³. The void volume of the electrode layer is 16%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % hard carbon(HC; 99.5% purity, Ruifute Technology Ltd., Shenzhen, Guangdong, China),5 wt. % carbon black and 5 wt. % polyacrylonitrile in deionized water toform a slurry having a solid content of 50 wt. %. The slurry was coatedonto both sides of a copper foil having a thickness of 9 μm using atransfer coater with an area density of about 15 mg/cm². The coatedfilms on the copper foil were dried at about 50° C. for 2.4 minutes by a24-meter-long conveyor hot air dryer operated at a conveyor speed ofabout 10 meters/minute to obtain a negative electrode. The electrode wasthen pressed to increase the density of the coating and the density was1.78 g/cm³. The void volume of the electrode layer is 19%.

Example 2

Assembling of Electrode Assembly

The resulting cathode film and anode film of Example 1 were used toprepare the cathode and anode respectively by cutting into individualelectrode plates. An electrode assembly was prepared by stacking anodes,cathodes and separators interposed between the positive electrode andthe negative electrode in the open air with no control of humidity. Theseparator was a microporous membrane made of nonwoven PET fabric(obtained from MITSUBISHI PAPER MILLS LTD, Japan), which had a thicknessof 30 μm. The electrode assembly was dried in a vacuum oven inside aglove box under a pressure of 5×10³ Pa at 100° C. for 2 hours. Thedrying chamber was then filled with hot, dry air having a water contentof 5 ppm and a temperature of 90° C. The hot, dry air was retained inthe drying chamber for 15 minutes before evacuating the drying chamber.This cycle was repeated 10 times.

Moisture Contents of Electrode Assembly, Electrodes and Separator

The average values of moisture contents of the electrode assembly,electrodes and separator were 19 ppm, 9 ppm and 15 ppm respectively.

Assembling of Pouch-Type Battery

A pouch cell was assembled by packaging the dried electrode assembly ina case made of an aluminum-plastic laminated film. The cathode and anodeelectrode plates were kept apart by separators and the case waspre-formed. An electrolyte was then filled into the case holding thepacked electrodes in high-purity argon atmosphere with moisture andoxygen content <1 ppm. The electrolyte was a solution of LiPF₆ (1 M) ina mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) anddimethyl carbonate (DMC) in a volume ratio of 1:1:1. After electrolytefilling, the pouch cells were vacuum sealed and then mechanicallypressed using a punch tooling with standard square shape.

Electrochemical Measurements of Example 2

I) Nominal Capacity

The cell was tested galvanostatically at a current density of C/2 at 25°C. on a battery tester (BTS-5V20A, obtained from Neware Electronics Co.Ltd, China) between 3.0 V and 4.2 V. The nominal capacity was about 2.6Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 1. The capacityretention after 486 cycles was about 94.7% of the initial value. Theelectrochemical tests show good electrochemical stability of the batteryin a wide range of potential, as well as outstanding cycle performance.

Example 3

A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 92 wt. % cathodematerial (LiMn₂O₄ obtained from HuaGuan HengYuan LiTech Co. Ltd.,Qingdao, China), 4 wt. % carbon black (SuperP; obtained from Timcal Ltd,Bodio, Switzerland) as a conductive agent, and 4 wt. % polyvinylidenefluoride (PVDF; Solef® 5130, obtained from Solvay S.A., Belgium) as abinder, which were dispersed in N-methyl-2-pyrrolidone (NMP; purity of≥99%, Sigma-Aldrich, USA) to form a slurry with a solid content of 50wt. %. The slurry was homogenized by a planetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm using a transfer coater with an area densityof about 40 mg/cm². The coated films on the aluminum foil were dried for6 minutes by a 24-meter-long conveyor hot air drying oven as asub-module of the transfer coater operated at a conveyor speed of about4 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of65° C. to the outlet temperature of 80° C. The electrode was thenpressed to increase the density of the coating and the density was 3.01g/cm³. The void volume of the electrode layer is 25%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % of hardcarbon (HC; purity of 99.5%, obtained from Ruifute Technology Ltd.,Shenzhen, Guangdong, China) with 1.5 wt. % carboxymethyl cellulose (CMC,BSH-12, DKS Co. Ltd., Japan) and 3.5 wt. % SBR (AL-2001, NIPPON A&LINC., Japan) as a binder, and 5 wt. % carbon black as a conductiveagent, which were dispersed in deionized water to form another slurrywith a solid content of 50 wt. %. The slurry was coated onto both sidesof a copper foil having a thickness of 9 μm using a transfer coater withan area density of about 15 mg/cm². The coated films on the copper foilwere dried at about 50° C. for 2.4 minutes by a 24-meter-long conveyorhot air dryer operated at a conveyor speed of about 10 meters/minute toobtain a negative electrode. The electrode was then pressed to increasethe density of the coating and the density was 1.78 g/cm⁻³. The voidvolume of the electrode layer is 19%.

Example 4

Assembling of Electrode Assembly

The resulting cathode film and anode film of Example 3 were used toprepare the cathode and anode respectively by cutting into individualelectrode plates. An electrode assembly was prepared by stacking anodes,cathodes and separators interposed between the positive electrode andthe negative electrode in the open air with no control of humidity. Theseparator was a ceramic coated microporous membrane made of nonwovenfabric (SEPARION, Evonik Industries, Germany), which had a thickness ofabout 35 μm. The electrode assembly was dried in a vacuum oven inside aglove box under a pressure of 10×10³ Pa at 102° C. for 3 hours. Thedrying chamber was then filled with hot, dry nitrogen having a watercontent of 5 ppm and a temperature of 85° C. The hot, dry air wasretained in the drying chamber for 5 minutes before evacuating thedrying chamber. This cycle was repeated 10 times.

Moisture Contents of Electrode Assembly, Electrodes and Separator

The average values of moisture contents of the electrode assembly,electrodes and separator were 33 ppm, 12 ppm and 26 ppm respectively.

Electrochemical Measurements of Example 4

I) Nominal Capacity

A pouch cell containing the dried electrode assembly prepared by methoddescribed in Example 4 was assembled according to the method describedin Example 2. The cell was tested galvanostatically at a current densityof C/2 at 25° C. on a battery tester between 3.0 V and 4.2 V. Thenominal capacity was about 9.3 Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 2. The capacityretention after 448 cycles was about 95.1% of the initial value. Theelectrochemical tests show the good electrochemical stability of thebattery in a wide range of potential, as well as outstanding cycleperformance.

Example 5

A) Preparation of Positive Electrode Slurry

A positive electrode slurry was prepared by mixing 94 wt. % cathodematerial LiNi_(0.33)Mn_(0.33)CO_(0.33)O₂ (obtained from ShenzhenTianjiao Technology Co. Ltd., China), 3 wt. % carbon black (SuperP;obtained from Timcal Ltd, Bodio, Switzerland) as a conductive agent, and1.5 wt. % polyacrylic acid (PAA, #181285, obtained from Sigma-Aldrich,US) and 1.5 wt. % polyacrylonitrile (LA 132, Chengdu Indigo PowerSources Co., Ltd., China) as a binder, which were dispersed in deionizedwater to form a slurry with a solid content of 50 wt. %. The slurry washomogenized by a planetary stirring mixer.

B) Preparation of Positive Electrode

The homogenized slurry was coated onto both sides of an aluminum foilhaving a thickness of 20 μm using a transfer coater with an area densityof about 32 mg/cm². The coated films on the aluminum foil were dried for4 minutes by a 24-meter-long conveyor hot air drying oven as asub-module of the transfer coater operated at a conveyor speed of about6 meters/minute to obtain a positive electrode. Thetemperature-programmed oven allowed a controllable temperature gradientin which the temperature gradually rose from the inlet temperature of60° C. to the outlet temperature of 75° C. The electrode was thenpressed to increase the density of the coating and the density was 2.65g/cm³. The void volume of the electrode layer is 34%.

C) Preparation of Negative Electrode

A negative electrode slurry was prepared by mixing 90 wt. % hard carbon,5 wt. % carbon black and 5 wt. % polyacrylonitrile in deionized water toform a slurry having a solid content of 50 wt. %. The slurry was coatedonto both sides of a copper foil having a thickness of 9 μm using atransfer coater with an area density of about 15 mg/cm². The coatedfilms on the copper foil were dried at about 50° C. for 2.4 minutes by a24-meter-long conveyor hot air dryer operated at a conveyor speed ofabout 10 meters/minute to obtain a negative electrode. The electrode wasthen pressed to increase the density of the coating and the density was1.78 g/cm³. The void volume of the electrode layer is 19%.

Example 6

Assembling of Electrode Assembly

The resulting cathode film and anode film of Example 5 were used toprepare the cathode and anode respectively by cutting into individualelectrode plates. An electrode assembly was prepared by stacking anodes,cathodes and separators interposed between the positive electrode andthe negative electrode in the open air with no control of humidity. Theseparator was a microporous membrane made of polyimide (Jiangxi AdvancedNanofiber Technology Co., Ltd., China) having a thickness of 20 μm. Theelectrode assembly was dried in a vacuum oven inside a glove box under apressure of 1×10³ Pa at 110° C. for 2 hours. The drying chamber was thenfilled with hot, dry air having a water content of 5 ppm and atemperature of 100° C. The hot, dry air was retained in the dryingchamber for 10 minutes before evacuating the drying chamber. This cyclewas repeated 10 times.

Moisture Content of Electrode Assembly

The average value of moisture content of the electrode assembly was 16ppm. Electrochemical measurements of Example 6

I) Nominal Capacity

A pouch cell containing the dried electrode assembly prepared by methoddescribed in Example 6 was assembled according to the method describedin Example 2. The cell was tested galvanostatically at a current densityof C/2 at 25° C. on a battery tester between 3.0 V and 4.2 V. Thenominal capacity was about 8.5 Ah.

II) Cyclability Performance

The cyclability performance of the pouch cell was tested by charging anddischarging at a constant current rate of 1 C between 3.0 V and 4.2 V.Test result of cyclability performance is shown in FIG. 3. The capacityretention after 598 cycles was about 93.8% of the initial value. Theelectrochemical tests show the good electrochemical stability of thebattery in a wide range of potential, as well as outstanding cycleperformance.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. Variations andmodifications from the described embodiments exist. The appended claimsintend to cover all those modifications and variations as falling withinthe scope of the invention.

What is claimed is:
 1. An electrode assembly for a lithium-ion battery,comprising at least one anode, at least one cathode and at least oneseparator interposed between the at least one anode and at least onecathode, wherein the at least one anode comprises an anode currentcollector and an anode electrode layer comprising an anode material anda binder material, and the at least one cathode comprises a cathodecurrent collector and a cathode electrode layer comprising a cathodematerial and a binder material; wherein each of the cathode and anodeelectrode layers independently has a void volume between 10% and 35%,based on the total volume of the electrode layer; wherein the amount ofeach of the binder materials is independently at least 3% by weight,based on the total weight of the electrode layer; wherein the at leastone separator is made of polymeric fibers selected from the groupconsisting of polyamide, polycarbonate, polyimide, polyetheretherketone, polysulfones, polyphenylene oxide, polyphenylene sulfide,polyacrylonitrile, polyvinyl pyrrolidone, polyester, polyethyleneterephthalate, polybutylene terephthalate, polyethylene naphthalene,polybutylene naphthalate, and combinations thereof; wherein the watercontent of the electrode assembly is less than 20 ppm by weight, basedon the total weight of the electrode assembly; wherein the cathodeelectrode layer and the anode electrode layer each further comprisesonly one conductive agent independently selected from the groupconsisting of carbon, carbon black, graphite, expanded graphite,graphene, graphene nanoplatelets, carbon fibers, carbon nano-fibers,graphitized carbon flake, carbon tubes, carbon nanotubes, activatedcarbon and mesoporous carbon; wherein the density of each of the cathodeand anode electrode layers is independently from 1.0 g/cm³ to 6.5 g/cm³,and wherein each of the binder materials is independently selected fromthe group consisting of styrene-butadiene rubber, acrylatedstyrene-butadiene rubber, acrylonitrile copolymer,acrylonitrile-butadiene rubber, nitrile butadiene rubber,acrylonitrile-styrene-butadiene copolymer, acryl rubber, butyl rubber,fluorine rubber, polytetrafluoroethylene, polyethylene, polypropylene,ethylene/propylene copolymers, polybutadiene, polyethylene oxide,chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine,polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin,polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resins,phenolic resins, epoxy resins, carboxymethyl cellulose, hydroxypropylcellulose, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylcellulose, cyanoethylsucrose, polyester,polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid,polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate,polyacrylamide, polyurethane, fluorinated polymer, chlorinated polymer,a salt of alginic acid, polyvinylidene fluoride, poly(vinylidenefluoride)-hexafluoropropene, and combinations thereof.
 2. The electrodeassembly of claim 1, wherein the density of each of the cathode andanode electrode layers is independently from 1.0 g/cm³ to 3.0 g/cm³. 3.The electrode assembly of claim 1, wherein the thickness of each of thecathode and anode electrode layers is independently from 1.0 μm to 40μm.
 4. The electrode assembly of claim 1, wherein the thickness of eachof the cathode and anode electrode layers is independently from 1.0 μmto 25 μm.
 5. The electrode assembly of claim 1, wherein the thickness ofthe separator is from about 1.0 μm to about 40 μm.
 6. The electrodeassembly of claim 1, wherein the thickness of the separator is fromabout 1.0 μm to about 25 μm.
 7. The electrode assembly of claim 1,wherein each of the binder materials in the cathode and anode electrodelayers is independently present in an amount from 3% to 10% by weight,based on the total weight of the electrode layer.
 8. The electrodeassembly of claim 1, wherein the cathode material is selected from thegroup consisting of LiCoO₂, LiNiO₂, LiNi_(x)Mn_(y)O₂,Li_(1+z)Ni_(x)Co_(1−x−y)O₂, LiNi_(x)Co_(y)Al_(z)O₂, LiV₂O₅, LiTiS₂,LiMoS₂, LiMnO₂, LiCrO₂, LiMn₂O₄, LiFeO₂, LiFePO₄, and combinationsthereof, wherein each x is independently from 0.3 to 0.8; each y isindependently from 0.1 to 0.45; and each z is independently from 0 to0.2.
 9. The electrode assembly of claim 1, wherein each of theconductive agents in the cathode and anode electrode layers isindependently present in an amount from 2% to 10% by weight, based onthe total weight of the electrode layer.
 10. The electrode assembly ofclaim 1, wherein the anode material is selected from the groupconsisting of natural graphite particulate, synthetic graphiteparticulate, Sn particulate, Li₄Ti₅O₁₂ particulate, Si particulate, Si—Ccomposite particulate, and combinations thereof.
 11. The electrodeassembly of claim 1, wherein each of the current collectors of the atleast one cathode and anode is independently stainless steel, titanium,nickel, aluminum, copper, or electrically-conductive resin.
 12. Theelectrode assembly of claim 1, wherein the current collector of the atleast one cathode is an aluminum film, and wherein the current collectorof the at least one anode is a copper film.
 13. The electrode assemblyof claim 1, wherein the at least one anode and at least one cathode inthe electrode assembly have a water content of less than 20 ppm byweight, based on the total weight of the at least one anode and at leastone cathode.
 14. The electrode assembly of claim 1, wherein the at leastone separator in the electrode assembly has a water content of less than20 ppm by weight, based on the total weight of the at least oneseparator.
 15. A lithium-ion battery comprising the electrode assemblyof claim 1.